Endometriosis is one of the most common gynecological disorders, affecting up to 15% of women of reproductive age. It is associated with severe pelvic pain, infertility, dysmenorrhea, dyspareunia, and several other symptoms such as intraperitoneal bleeding, back pain, constipation and/or diarrhea. It is a major threat to physical, psychological and social integrity of the patients.
Endometriosis is characterized by the implantation and growth of endometrial cells (which normally constitute the lining of the uterus) in extra-uterine sites such as the peritoneal cavity. Although the etiology and pathogenesis of endometriosis remain mainly unclear, the theory of retrograde menstruation is the most widely accepted to explain the presence of ectopic endometrial cells in the peritoneal cavity. However, this phenomenon occurs in most women and, thus, several other factors must be invoked to explain the implantation of endometrial cells and the subsequent development of endometriotic lesions. It is generally believed that initiation of endometriosis implies a complex cascade of events requiring several essential features. Retrogradely seeded endometrial cells must remain viable, be capable of adhering to the mesothelium and of proliferating. Local degradation of the extracellular matrix, as well as extensive vascularization, are also believed to play an essential role in promoting the invasion of the peritoneal cavity by endometrial cells. Furthermore, once implanted, ectopic endometrial cells must have the capacity to counteract the cytolytic action of the immune system. Indeed, this is supported by the observation of several immunological abnormalities in patients with endometriosis.
At present, direct visualization of the endometriotic lesions under surgical procedures (laparascopy or laparotomy) is the golden standard and the only reliable method available to diagnose endometriosis. However, this method is highly invasive (i.e. surgery under general anesthesia), costly (i.e. direct cost and indirect cost due to convalescence) and requires a well-trained surgeon who has the ability to identify endometriotic lesions with a variety of appearances. The type of lesions, their size and their localization will determine the stage of the disease (stage I minimal, stage II mild, stage III moderate, stage IV severe). However, there is still no clear consensus on how these parameters correlate with the stage of the disease and the prognostic of endometriosis. In addition, early or minimal endometriosis (which can involve microlesions) can be hardly diagnosed by surgical methods, as they are unlikely to be detected by direct visualization. Indeed, several studies have reported microscopic endometriotic lesions that were not detected laparoscopically. Because the diagnosis of endometriosis by surgical procedures is difficult, costly and invasive, in some cases, several physicians and patients tend to avoid it or at least seriously delay it. Hence, the length of time between the onset of symptoms and the diagnosis can be as long as 8 to 12 years. The possibility to diagnose endometriosis at an early stage would certainly improve the efficacy of the treatments, and reduce dramatically the number of years during which patients endure acute or chronic pain.
Effective methods to treat or prevent endometriosis are lacking, and thus, there is a need for new therapeutics.